Benzene

Benzene is
an organic chemical compound with the molecular formula C₆H₆.Benzene
is a colorless and highly flammable liquid with a sweet smell and a relatively
high melting point. Because it is a known carcinogen, its use as an additive in
gasoline is now limited, but it is an important industrial solvent and precursor
in the production of drugs, plastics, synthetic rubber, and dyes. Benzene is a
natural constituent of crude oil, and may be synthesized from other compounds
present in petroleum.The word "benzene" derives historically from
"gum benzoin", sometimes called "benjamin" (i.e., benzoin
resin), an aromatic resin known to European pharmacists and perfumers since the
15th century as a product of southeast Asia.

Ring
formula

The empirical formula for benzene was long known,
but its highly polyunsaturated structure, with just one hydrogen atom for each
carbon atom, was challenging to determine.

A scientist show in his dreams that a snake was
eating it's own tial;, so he supposed the benzene may be ring in structure and
it did not show the test of alken and alkenes so that it was difficult for them
to describe benzene under the group of alken or alkenes, but the ring structure
made it to easily understable for scientist.

Structure

The C–C bond lengths are greater than a double
bond (135pm) but shorter than a single bond (147pm). This intermediate distance
is explained by electron delocalisation: the electrons for C–C bonding are
distributed equally between each of the six carbon atoms. One representation is
that the structure exists as a superposition of so-called resonance structures,
rather than either form individually. This delocalisation of electrons is known
as aromaticity, and gives benzene great stability. This enhanced stability is
the fundamental property of aromatic molecules that differentiates them from
molecules that are non-aromatic.Realising each carbon has 2p electrons, each
carbon donates an electron into the delocalised ring above and below the benzene
ring. It is the side-on overlap of p-orbital that produces the pi clouds.

Production

benzene produced from toluene. In this
hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a
chromium, molybdenum, or platinum oxide catalyst at 500–600 °C and 40–60
atm pressure.

C₆H₅CH₃ + H₂
→ C₆H₆ + CH₄

This irreversible reaction is accompanied by an
equilibrium side reaction that produces biphenyl (aka biphenyl) at higher
temperature:

2 C₆H₆→ 
H₂ + C₆H₅–C₆H₅